1. Field of the Invention
The present invention relates to fluid conveyance devices and, in particular, to a fluid conveyance device utilizing a bending piezoelectric element.
2. Description of the Related Art
A piezoelectric pump has been used as a coolant water pump for a compact electronic apparatus, such as a notebook personal computer, and a fuel transport pump for a fuel cell, for example. The piezoelectric pump is also used as a fan pump which replaces a cooling fan for a CPU or other electronic apparatus, or a fan pump for supplying oxygen required by a fuel cell that generates power. The piezoelectric pump is a pump that utilizes a piezoelectric element that bends into a shape thereof in response to voltage application. The advantages of the piezoelectric pump are a simple and thin structure and low power consumption.
Japanese Unexamined Patent Application Publication No. 2-149778 and Japanese Unexamined Patent Application Publication No. 4-86388 disclose piezoelectric pumps. In the piezoelectric pumps, a vibration plate is arranged in contact with a pump body having an inlet port and an outlet port, and a plurality of piezoelectric elements are arranged from the inlet port to the outlet port on the vibration plate. In this pump, when the piezoelectric elements arranged from the inlet portion to the outlet port are successively driven, the vibration plate is bent, one portion after another, from the inlet port to the outlet port so that a fluid is pushed from the inlet port to the outlet port. When voltage applied to the piezoelectric element stops, a flow passage between the inlet port and the outlet port is closed in response to a recovery of the vibration plate. Therefore, a check valve between the inlet port and the outlet port is not required.
In the above-described related art, the piezoelectric pump includes the plurality of bonded piezoelectric elements which have voltages that are different in phases applied thereto, and thus, operates as a tube pump which conveys a fluid from one end to the other end of the pump body. Since the plurality of piezoelectric elements are arranged in a plane, the pump has a bulky and complex structure. Since the plurality of piezoelectric elements operate in a tube-pump mode, the structure of an elastically deformable joint connecting the piezoelectric elements and sealing of the fluid presents difficulties. A mechanism for conveying a miniature volume pocket holding the fluid is also difficult to implement.
Japanese Unexamined Patent Application Publication No. 1-500892 discloses a fluid pump which includes ring segment electrodes provided on each of a central portion and a periphery portion of a piezoelectric element. The central portion and the periphery portion are expanded and contracted in opposite directions to bend the piezoelectric element and thus functions as a pump to convey a fluid. The piezoelectric element is rectangular, and segment electrodes are arranged in a longitudinal direction of the piezoelectric element. In this case, the bending shape of the piezoelectric element is also in a tube-pump mode in which the piezoelectric element bends from one end to the other end. As in the above-described related art, a plurality of electrodes must be arranged in the direction of motion, and the pump has a bulky structure. Sealing of a joint connecting the elastically deformable electrodes is also difficult.
A miniature volume pocket containing the fluid is also difficult to convey.